Thursday, March 24, 2016

Gyroscope L3G4200D

L3G4200D is a MEMS ultra-stable three-axis digital output gyroscope made by STMicroelectronics. A L3G4200D Module in Aliexpress costs only about $3.


Figure. L3G4200 Gyroscope module


That module (see details) already consists of pull up resistors, and 3.3V QT33 LDO regulator, therefore, connecting its Vcc with 5V is ok. Arduino Uno uses 5V and an example schematic for that module is shown below.


Figure. Schematic for connecting Arduino Uno and L3G4200.



Figure. Breadboard view for connecting L3G4200 module to Arduino Uno.


The latest version Arduino IDE has serial plotter, and the readings from Gyroscope can be plotted directly on serial plotter. An example program for L3G4200 with Arduino - GitHub is shown below.

#include <SPI.h>
const int CS_Pin = 10;// set pin 10 as the chip select
//SPI pin configuration: pin 11 as MOSI (SDI), pin 12 as MISO (SDO) , pin 13 as clock (SPC)

int x,y,z;
float K=8.75; // 8.75 mdps per digit for +/-250dps full scale using 16 bit digital output

void setup() {
  Serial.begin(115200);
  pinMode (CS_Pin, OUTPUT);  //Chip Select pin to control SPI
  digitalWrite(CS_Pin, HIGH);//Disable SPI
  SPI.begin();
  SPI.setBitOrder(MSBFIRST);
  SPI.setDataMode(SPI_MODE3);

  //b7 = set (1) for reading 
  //b6 = cleared (0) not to auto increase address 
  //b5-b0 = register address
  
  //digitalWrite(CS_Pin, LOW);//Enable SPI
  //-------------------------------------------------------------------------
  //SPI.transfer(0x8F);//Read 'Who am I?' register
  //x=SPI.transfer(0x00);//Get return value of Who am I
  //-------------------------------------------------------------------------
  //digitalWrite(CS_Pin, HIGH);//Disable SPI
  
  digitalWrite(CS_Pin, LOW);//Enable SPI
  //-------------------------------------------------------------------------
  //CTRL_REG2 = |0 |0 |HPM1|HPM0|HPCF3|HPCF2|HPCF1|HPCF0|
  //Default =   |0 |0 |0   |0   |0    |0    |0    |0    |
  //HPM = 00 => Normal (High Pass filter Mode selection)
  //HPC = 1001 => 0.1 High Pass Filter Cut-off freq configuration
  SPI.transfer(0x21);//address 
  SPI.transfer(0x09);//register value to write
  //-------------------------------------------------------------------------
  digitalWrite(CS_Pin, HIGH);//Disable SPI
  
  //-------------------------------------------------------------------------
  //CTRL_REG3 = |I1_Int1|I1_Boot|H_Lactive|PP_OD|I2DRDY|I2_WTM|I2_ORun|I2_Empty|
  //Default =   |0      |0      |0        |0    |0     |0     |0      |0       |
  //Use Default
  //-------------------------------------------------------------------------
  
  digitalWrite(CS_Pin, LOW);//Enable SPI
  //-------------------------------------------------------------------------
  //CTRL_REG4 = |BDU|BLE|FS1|FS0| - |ST1|ST0|SIM|
  //Default =   |0  |0  |0  |0  |0  |0  |0  |0  |
  //BDU = 1 => Block Data Update
  //BLE = 0 => Little endian 
  //FS = 00 => 250 dps (Full scale selection)
  //ST = 000 => Disable Self test
  SPI.transfer(0x23);//address 
  SPI.transfer(0x80);//register value to write
  //-------------------------------------------------------------------------
  digitalWrite(CS_Pin, HIGH);//Disable SPI

  //-------------------------------------------------------------------------
  //CTRL_REG5 = |BOOT|FIFO_EN| - |HPen|INT1_Sel1|INT1_Sel0|Out_Sel1|Out_Sel0|
  //Default =   |0   |0      |0  |0   |0        |0        |0       |0       |
  //BOOT = 0 => Normal mode (Reboot Memory Content)
  //FIFO_EN = 0 => disable FIFO 
  //HPen = 0 => disable (High Pass Filter)
  //INT1_Sel = 00 => Non high pass filtered data are used for interrupt generation
  //Out_Sel = 00 => no filtering
  //Use Default
  //-------------------------------------------------------------------------
  
  digitalWrite(CS_Pin, LOW);//Enable SPI
  //-------------------------------------------------------------------------
  //CTRL_REG1 = |DR1|DR0|BW1|BW0|PD|Zen|Yen|Xen|
  //Default =   |0  |0  |0  |0  |0 |1  |1  |1  |
  //DR = 11 => ODR 800 Hz (output data rate)
  //BW = 10 => Cut-off 50 (Bandwidth 50 Hz)
  //PD = 1 => Normal
  //Zen = Yen = Xen = 1 => Enable
  SPI.transfer(0x20);//address
  SPI.transfer(0xEF);// data rate 800, BW 50Hz, enable all axes
  //-------------------------------------------------------------------------
  digitalWrite(CS_Pin, HIGH);//Disable SPI
}

void loop() {
  delay(10);
  digitalWrite(CS_Pin, LOW);//Enable SPI
  SPI.transfer(0xE8);//Send address of LSB of x. Address is auto-increased after each reading.
  x = SPI.transfer(0) | SPI.transfer(0)<<8; //x axis 
  y = SPI.transfer(0) | SPI.transfer(0)<<8; //y axis
  z = SPI.transfer(0) | SPI.transfer(0)<<8; //z axis
  digitalWrite(CS_Pin, HIGH);//Disable SPI
  Serial.println(String(K*x)+" "+String(K*y)+" "+String(K*z));
}


When the Gryroscope module is rotated in each axis, the varying outputs can be seen on serial plotter as illustrated below. I used a rubber band to tie Arduino borad to prevent it from dropping off when shaking :P


Figure. Serial plotter shows changes as the module is rotated in its axes.



Figure. My experiment setup.


Examples to read accelerometers and a gyroscope using NXP LPC54102 dual core ARM microcontroller and 8051 microcontroller can be seen together at the following link.

Reading IMU in C on GitHub


Figure. A gyroscope and 4 accelerometers on the bottom side, and a dual core ARM microcontroller on top side of an in-house built embedded circuit board (Ø < 1 in).



Figure. An embedded inertial measurement unit using LPC54102 ARM microcontroller.



Figure. Schematic for gyroscope.





Figure. An embedded inertial measurement unit using an 8051 microcontroller.


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